Breast-conserving surgery, or lumpectomy, is the most common surgical procedure for patients diagnosed with an early stage of invasive breast cancer. Clearly defined tumor margins and complete surgical removal of tumors are critical for preventing local recurrence and increasing disease-free survival. Currently, there is no accurate method to identify tumor margins pre- or intra-operatively. About 20% to 30% of the patients who undergo lumpectomy require additional surgery to excise any remaining tumors due to the presence of positive tumor margins. To develop a sensitive approach for detecting tumor margins in breast tissues, we propose to engineer a tumor targeted nanoparticle imaging probe by labeling a peptide containing the receptor binding domain (ATF) of urokinase plasminogen activator (uPA) with a near infrared (NIR) dye and then conjugating these complexes to a magnetic iron oxide (IO) nanoparticle. The objectives of this proposed study are: 1) to develop new NIR optical imaging nanoprobes targeting the cellular receptor for uPA; 2) to develop a sensitive fluorescence tomography system for imaging-guided surgery aimed at completely removing tumor lesions within breast tissue; and 3) to examine the effect of the optical imaging guided resection of mammary tumors on local tumor recurrence and metastasis in a mouse mammary tumor model. The development of novel tumor targeted NIR imaging nanoprobes, in combination with a sensitive and high resolution NIR fluorescence tomography system, should have great potential for determining tumor margins during surgery, preventing tumor recurrence and therefore, increasing the survival rate of breast cancer patients. PUBLIC HEALTH RELEVANCE The objective of this proposed study is to develop a novel optical imaging approach that combines tumor targeted optical imaging probes with advanced optical imaging instrumentation for the detection of breast cancer and for outlining the tumor border during breast conserving surgery. In this study, we will develop urokinase plasminogen activator receptor (uPAR) targeted near infrared (NIR) dye-labeled nanoparticles to deliver the imaging probes into breast tumors, the location and depth of the tumors will be detected using 3D diffuse fluorescence tomography. Success in this proposed study should provide us with novel optical imaging agents as well as instruments to address the urgent need for preventing tumor recurrence after breast conserving surgery and ultimately, to improve the survival rate of breast cancer patients.